In one aspect, this invention pertains to a process for the production of alkylated benzenes by alkylating benzene with an alkylating agent or by transalkylating benzene with a transalkylating agent in the presence of a catalytic zeolite. In another aspect, this invention pertains to a method of increasing the lifetime of a zeolite alkylation/transalkylation catalyst.
Alkylation and transalkylation processes employing zeolite catalysts are useful for producing monoalkylated and dialkylated benzenes. Monoalkylated benzenes, such as ethylbenzene and cumene, are highly valuable bulk chemicals. Ethylbenzene, for example, is used in the preparation of styrene, a precursor to polystyrene. Cumene is used in the preparation of phenol and acetone. Dialkylated benzenes, such as para-di(isopropyl)benzene, are useful starting materials for preparing the corresponding dicarboxylic acid or dihydroxy benzenes, for example, hydroquinone.
It is known to alkylate benzene with an olefin in the presence of a catalytic zeolite. With regard to the use of dealuminated acid mordenite zeolite, reference is made to U.S. Pat. Nos. 4,891,448, 5,198,595, 5,243,116, and European Patent publication 0,366,515. With regard to the use of zeolite ZSM-5, reference is made, for example, to U.S. Pat. No. 4,665,255. With regard to the use of zeolite beta, reference is made to U.S. Pat. Nos. 4,891,458, and 5,081,323.
It is known that the lifetime of a zeolite alkylation catalyst is shortened by polymerization of the olefinic alkylating agent and by formation of carbonaceous deposits (polyaromatics). Periodically, an alkylation reactor, whether operating in a liquid or gas phase, must be shut down to regenerate the catalyst. Regeneration is typically effected by controlled burning off of the condensed polymers and carbonaceous deposits in air at elevated temperature, for example, at a temperature between about 400.degree. C. and about 700.degree. C. Disadvantageously, repeated regeneration at elevated temperatures can damage the zeolite.
It is known, for example, from PCT application WO 89/12613, that the lifetime of an alkylation catalyst can be improved by adding hydrogen to the alkylation feedstream. Disadvantageously, this process requires a hydrogen supply which increases expenses and necessitates a complex engineering design.
Some patents, such as PCT application WO 93/00992, disclose the addition of water to an alkylation feed or alkylation/transalkylation molecular sieve catalyst to increase the lifetime of the catalyst. In contrast, other patents, such as U.S. Pat. No. 5,030,786, teach an increase in catalyst lifetime on decreasing the concentration of water in the alkylation feedstream.
It is also known, such as from U.S. Pat. Nos. 4,358,362 and 5,245,094, to enhance the activity of a zeolite catalyst employed in a catalytic conversion process by pretreating the process feedstock over a molecular sieve zeolite. This method has been illustrated for pretreating hydrocarbon feedstocks used in dewaxing processes and for pretreating C.sub.6-20 olefinic feedstocks derived from the dehydrogenation of long-chain paraffins, for use in alkylation processes.
It would be advantageous to find an effective method for improving the lifetime of a zeolite catalyst employed in an alkylation or transalkylation process, preferably for preparing ethylbenzene or cumene. It would be more advantageous if the regeneration method could be used without damage to the catalyst and without undue expense and complex engineering.